Nesting three dimensional lazy tong structure

ABSTRACT

A nesting three-dimensional lazy tong structure of hollow polygonal cross-section having tapered sides provided by lazy tong frames whose hinged links are pivotally joined and crossover one another in a manner such that the successive link sets or tiers of the structure nest one within the other when the structure is retracted to its contracted configuration to provide the structure with a contracted length approximating the contracted dimension of a single link set or tier. A lazy tong frame and link pair for the structure.

United States Patent Luckey 51 June 27, 1972 s41 NESTING THREE DIMENSIONAL LAZY 1,947,647 2/1934 Holden ..1s2/14| TONG STRUCTURE FOREIGN PATENTS on APPLICATIONS [72] Inventor: George R. Lucltey, Playa Del Rey, Calif.

[73] Assignee: TRW lnc., Redondo Beach, Calif.

[22] Filed: Dec. 23, 1970 [21] Appl. No.: 100,912

[52] U.S. Cl 52/109, 52/646, 182/141, 248/277 [51] Int. Cl ..E04h 12/10 [58] Field oISearch ..52/l09, 645,108, 646,14/45', 74/521; 182/69, 141; 187/18; 248/277 [56] References Cited UNITED STATES PATENTS 2,299,687 10/1942 Farrand ..52/l09 797,077 8/1905 Shaw ..52/l09 3,053,351 9/1962 Fulcher................. .....52/122 1,592,770 7/1926 Liberman ..l82/l4l 1,419,013 10/1965 France ..52/l09 Primary ExaminerFrank L. Abbott Assistant Examiner-Leslie A. Braun Attorney-Daniel T. Anderson, Donald R. Nyhagen and Jerry A. Dinardo 57 ABSTRACT A nesting three-dimensional lazy tong structure of hollow polygonal cross-section having tapered sides provided by lazy tong frames whose hinged links are pivotally joined and crossover one another in a manner such that the successive link sets or tiers of the structure nest one within the other when the structure is retracted to its contracted configuration to provide the structure with a contracted length approximating the contracted dimension of a single link set or tier. A lazy tong frame and link pair for the structure.

10 Claims, 6 Drawlng Figures PATENTEUJUHET m2 SHEET 10? 3 Fig! George R. Luckey INVENTOR.

ATTORNEY FATENTEDJUHE? m2 3.672.104 sum 2 BF 3 George R. Luckey INVENTOR ZLM/y ATTORNEY PATENTEnJum m2 SHEEI 3 OF 3 George R. Luckey INVENTOR.

ATTORNEY NES'IING THREE DIMENSIONAL LAZY TONG STRUCTURE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to extensible and contractsble structures and more particularly to a novel nesting threedimensional lazy tong structure. The invention relates also to a lazy tong frame and hinged link pair for the structure.

2. Prior Art Many applications exist and other applications continuously arise for towers, booms and the like which can be retracted to a compact stowage configuration and extended to a relative great height or length for use. Numerous examples of such structures exist in the prior art. Typical of such prior art structures, for example, are those disclosed in US. Pat. Nos. 797,077; 1,947,647; 2,299,687; and 3,053,351.

Of major importance in the design of such structures is their ratio of extended to contracted length. In most, if not all applications, this ratio should be as large as possible. That is to say, the contracted length should be relatively small and the extended length should be relatively large. As a general rule, the larger this ratio, the smaller will be the weight of the structure per unit deployed length. While weight may not be critical in many applications, it is extremely important in others, such as space applications.

Extensible structures of the class described vary widely in construction. The present invention is concerned with deployable structures of the general type disclosed in the earlier mentioned prior art patents which employ, essentially, a threedimensional lazy tong construction consisting of hinged link sets pivotally joined to one another. The prior art structures of this kind suffer from the disadvantage that contraction of the structure is limited by edge to edge abutment of the links of adjacent link sets or tiers. As a consequence, the contracted length of the structure is effectively the summation of the contracted dimensions, along the deployment axis, of the several link tiers.

SUMMARY OF THE INVENTION The present invention provides an improved extensible structure of the class described which is uniquely constructed and arranged such that the successive hinged link sets or tiers nest or telescope one within the other when the structure is contracted. This nesting feature provides the structure with an effective contracted length approximating the contacted dimension, along the deployment axis, of a single link set or tier.

Like certain of the prior an extensible structures, the present extensible structure is essentially a three-dimensional lazy tong structure of hollow polygonal cross-section. The sides of the structure are furnished by similar lazy tong frames pivotally joined to one another along the longitudinal comers of the structure by corner brackets. The several frames define successive sets or tiers of hinged links, each including one pair of hinged links in each of the frames and comer brackets pivotally joining the corresponding link ends of the link pairs; that is to say each tier of the structure comprises the corresponding hinged link pairs in the several lazy tong frames and their respective corner brackets of the structure. Each link pair is composed of two links of equal length having center and end pivots and pivotally joined to one another at their center pivots. The center and end pivots of each link are located in a common longitudinal plane of the link.

According to the present invention, the links of the successive link pairs of each link frame, and hence the links of the successive link set or tiers of the structure, diminish in length toward one end of the structure. such that each frame tapers toward the latter end and the structure has a generally pyramidal configuration. Also the two hinged links of each link pair are longitudinally offset so that each link has along end at one side of the center link pivot and a short end at the opposite side of this pivot. The corresponding ends of the two links are located at opposite sides of the center pivot. The two links of each link pair are shaped such that the short end of one link crosses over the long end of the other link, and the links are rotatable on their center pivot axis to a folded or contracted configuration wherein the axis of the several link pivots are located in a common longitudinal plane of the links. In this folded configuration, the short ends of the two links are located at one side, hereafter referred to as the inner side, of a plane passing between the links at and normal to their center pivot and the long ends are located at the opposite side, hereafter referred to as the outer side, of the plane. Also, the end pivots on the short ends are located longitudinally inward of, i.e. closer to the center pivot that, the end pivots on the long ends. The corresponding end pivots are equally spaced from the center pivot.

In the overall deployable structure, the short ends of the links of each link pair of each lazy tong frame are pivotally joined to the outer sides of the long links of the adjacent link pair, in the direction of the small ends of the frame and structure, at the end pivots of the respective link ends. The adjacent corresponding pivotally joined link ends of the several link frames are pivotally joined by corner brackets to form the link sets or tiers of the structure.

The present structure is so arranged that when it contracts, the tiers of the structure nest one within the other in a manner such that the fully contracted structure has a length approximating the overall width dimension of a single tier in its contracted or folded configuration. Accordingly, the structure is characterized by a high ratio of extended length to contracted length.

According to another feature of the invention, each lazy tong frame has planar end links which are pivotally joined at their outer ends to the ends of the adjacent link pair and at their inner ends to one another. The pivotally joined inner ends of the planar end links at the large end of the structure are pivotally attached to a supporting base. A platform or other support for an object to be deployed with the structure is pivotally attached to the pivotally inner joined ends of the planar end links at the small end of the structure. The structure is thus retractable to stowed configuration against the base and is extendable outwardly from the base to deployed configuration.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: structure FIG. 1 is a side elevation of a present lazy tong structure in its extended configuration;

FIG. 2 is a plane view of the sturucture in its contracted configuration;

FIG. 3 is a side elevation of the contracted structure;

FIG. 4 is a section taken on line 4-4 in FIG. 2;

FIG. 5 is an enlarged perspective view of one link pair of the structure;

FIG. 6 is a top plan view of one hinged link pair.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings illustrate a nesting three-dimensional lazy tong structure 10 according to the invention. The particular structure shown is a three-sided pyramidal structure of generally triangular cross-section. However, it will become evident as the description proceeds that the structure may have four or more sides.

The sides of the structure 10 are provided by similar lazy tong frames 12. Each frame 12 includes a number of hinged link pairs 14 which are pivotally connected in the manner shown and described below to form a lazy tongs. Each link pair is composed of a pair of centrally hinged links l6, 18 of equal length. The links of successive link pairs in the direction of one end of the structure diminish in length such that each frame 12 is longitudinally tapered, and the structure, when extended, has a generally pyramidal configuration. Except for these differing lengths of their links the link pairs are identical. Accordingly, a description of one link pair will suffice for all. With this in mind, a link pair 14 will be described by reference to FIG. 5.

The two links l6, 18 of link pair 14 are fashioned from two similar relatively stiff, though resiliently flexible, straps or bars which are formed to somewhat different shapes, as described below. Each link has a planar central portion 20 with an enlargement or tongue 22 along and projecting edgewise beyond one edge 24 of the link and end tongues 26, 28 which also project beyond the link edge 24. The two links l6, 18 are inverted relative to one another and are disposed with their planar central portions 20 located side by side. The links are joined by a center pivot 30 and have end pivot holes 34, to receive pivots for joining the links to the links of an adjacent link pair of the respective lazy tong frame 12, as described below. The axes of the center pivot 30 and end pivot holes 34, 35 of each link are located in a common plane of the link. In the particular embodiment illustrated, the three pivot axes of each link are located in a common longitudinal link plane containing the link edge 24. The center and end pivot axes of the links, that is the axis of the center pivot 30 and end pivot holes 34, 35, parallel one another and extend normal to a plane parallel to and passing between the center link portions 20. This plane is hereafter referred to as an intervening plane.

As will appear from the ensuing description, when the several link pairs 14 are assembled to form the extensible structure 12, each link pair has an inner side facing the central axis of the structure and an opposite outer side. Terms such as inner," inwardly," outer," and outwardly" in the following description are referenced to these inner and outer sides of the link pair. In this regard, it is worthy of note at this point that each of the link pairs is assembled in the structure in a manner such that the planar center portions 20 of its links l6, 18 are located at the outer and inner sides, respectively, of the intervening plane passing between the center portions. For this reason, links 16 and 18 are hereafter referred to in places as outer and inner links, respectively.

Returning again to the typical link pair 14 of HO. 5, the center pivot 30 is closer to the link end pivot holes 34 than to the end pivot holes 35. Accordingly each link has a relatively short arm 36 and a relatively long arm 38. The links are bent in such a way that the short arm 36 of the outer link 16 turns inwardly across the intervening link plane and the long arm 38 of the inner link 18 turns outwardly across this plane. These link arms thus crossover one another, as shown, to locate the two link ends 26 at the inner side of the intervening link plane and the two link ends 28 at the outer side of the plane. The two inner link ends 26 and the two outer link ends 28 are located in common inner and outer planes, respectively, parallel to the intervening plane.

Referring to FIG. 1, the several link pairs 14 of each lazy tong frame 12 are pivotally joined by link end pivots 40 which extend through the link end pivot holes 34, 35. In this regard, it will be seen that the several link pairs are arranged with their inner link ends 26 nearest one end of the frame, i.e. the upper end of the frame in FIG. 1, and their outer link ends nearest the opposite end of the frame. The inner link ends 26 of each link pair are located directly opposite and outward of the outer link ends 28 of the adjacent link pair and are joined by pivots 40 to the latter link ends.

In addition to the link pairs 14, each lazy tong frame 12 has end link pairs 42 and 44 at its ends. The bottom ends link pair 42 has a pair of planar ends links 46, 48. One end of these end links are located outward of and joined by pivots to the outer link ends 38 of the adjacent bottom link pair 14. The opposite ends of the end links 46, 48 are joined by a pivot 52. The top end link pair 44 has a pair of planar end links 56, 58. One end of these end links are located inward of and joined by pivots 60 to the inner ends 26 of the adjacent top link pair 14. The opposite ends of the links are joined by pivots 62.

As noted earlier and shown in FIG. 1, the links of the successive link pairs of each lazy tong frame 12 diminish in length in the direction of one end of the frame, i.e. the upper end of put the frame in FIG. 1, as a consequence, each frame has a generally longitudinally tapered configuration and narrows in the direction of its upper end. The lower end links 46, 48 are equal in length to the lower long link arms 38 of the adjacent bottom link pair 14. Similarly, the upper short arms 36 of each link pair 14 are equal in length to the lower long arms 38 of the adjacent upper link pair 14, and the short arm of the top link pair 14 are equal in length to the top end links 56, 58.

The several center link pivots 30, 52, 62 of each lazy tong frame 12 are located in a common longitudinal plane of the frame. The corresponding end pivots 40, 50, 60 are located in common planes which converge in the direction of the upper end of the frame.

As noted earlier, and shown in the drawings, the three lazy tong frames 12 are arranged to form the three sides of the triangular pyramidal structure 10. The three frames are joined at their corresponding end pivots 40, 50, 60 by rigid generally V- shaped comer members or brackets 66. Each bracket 66 has sides arranged at an included angle of 60. As shown best in FIG. 1, the sides of each bracket are interposed between corresponding pivotally joined link ends of the adjacent frames and are pivotally attached to the respective ends by their end pivots 40, $0, or 60 as the case may be. The lower end links 46, 48 of the frames 12 are joined by their pivots 52 to mounting brackets 68 which may be attached to a supporting base 70. The upper end links 56, 58 are joined by their pivots 62 to a platform 72 for supporting an object to be deployed or extended away from and retracted toward the base.

From the foregoing description, it is evident that the three lazy tong frames 12 and their interconnecting brackets 66 form a three-dimensional lazy tong structure of hollow triangular cross-section. The structure is retracted toward the base '70 by hinging of the several links in lazy tong fashion at their several pivot points. The corresponding link pairs l4, 42, 44 of the three frames I2 constitute link sets or tiers of the structure 10. A highly unique and beneficial feature of the structure resides in the fact that during its retraction or contraction, these link sets or tiers telescope or nest one inside of the other, as shown in FIGS. 2 through 4. The structure is thus retractable to a fully contracted configuration (FIGS. 2 4) wherein the crossing link arms 36, 38 of the link pairs 14 abut along the link edges 24, and their several pivot axes are located in a common longitudinal plane of the links containing the link edges 24. Thus, the fully contracted structure has an overall length or height, measured along its extension axis, approximating the combined width of a folded link pair (FIGS. 3, 4). The structure thus has a large ratio of deployed or extended length to contracted or stowed length.

During deployment or extension of the structure 10, the corner brackets 66 move outwardly from the base 70 and inwardly a small amount toward the structure centerline. This inward movement of the brackets is proportional to their distance of movement from the base. The corner brackets are reacted from rotational motion and binding by the torsional stiffness of the frame links, such that the bracket sides remain parallel with their original positions and with each other during deployment. Any tendency for a comer bracket to twist from its normal position loads all four of its attached links in torsion. Thus, the links must be torsionally stiff. This torsional stiffness, plus the fact that side loads on the structural produce shear forces and moment couples in the comer bracket pivots, requires that these pivots have only one degree of rotational freedom, i.e. rotation on their pivot axes, so as to be able to load the links torsionally.

The differential inward movement of the corner brackets of the successive link sets or tiers introduces slight reflex bending in the links in directions perpendicular to their faces or from the bending loads. Therefore, the links must have bending stiffness in the planar loading direction but must be flexible in the normal-to-planar direction and must be torsionally stiff.

Deployment of the present lazy tong structure can be accomplished by several means. depending on the application.

For example, some or all of the pivot points of the structure may be equipped with springs which are connected to the adjacent links in such a way that the springs urge the structure to extended configuration. The structure may be retracted to stowed configuration in any convenient way, as by a cable and winch. Other possible deployment means include ball-screw actuators, hydraulic struts, or a bellows-type balloon inside the structure which would supply the thrust for deployment with the structure providing stability.

If desired, locking of the structure in stowed and/or deployed configuration may be accomplished by the inclusion of latches at the pivots. These may be releasable or nonreleasable depending on the application.

What is claimed as new in support of Letters Patent is:

1. A link pair for a lazy tong frame comprising:

a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions;

a center pivot joining said central link portions on a center pivot axis normal to said intervening plane;

each link having relatively short and long arms at opposite sides of said pivot;

said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one mother;

said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane;

said short arm end portions having end pivot means with pivot axes parallel to and equally spaced from said center pivot, and said long arm end portions having end pivot means with pivot axes parallel to and equally spaced from said center pivot, the pivot axes of each link being located in a common longitudinal plane of the respective link; and

said links being rotatable about said center pivot to folded positions wherein said pivot axes are located in a common longitudinal plane of said links.

2. A link pair according to claim 1 wherein:

said crossing link arms have surfaces which abut in said folded positions.

3. A link pair according to claim 2 wherein:

said surfaces comprise edge surfaces of said links located in said common planes containing the pivot axes of the respective links.

4. A lazy tong frame comprising:

a number of link pairs each including a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions;

a center pivot joining said central link portions on a center pivot axis normal to said intervening plane;

each link having relatively short and long arms at opposite sides of its center pivot, and said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one another;

said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane;

said link pairs being arranged end to end in lazy tong fashion with their center pivot axes parallel to one another and located in a common plane and with said short arm end portions of each link pair located opposite said long arm end portions of the adjacent link pair;

end pivots joining the adjacent link end portions of adjacent link pairs on end pivot axes parallel to said center pivot axes;

the corresponding end pivots of each link pair being equally spaced from the center pivot of the respective link pair, and the pivot axes of each link being located in a common longitudinal plane of the respective link;

said links diminishing in length in the direction of one end of the frame, whereby said frame is tapered and narrows in the direction of said one end, and the pivotally joined link arms of adjacent link pairs have equal length; and

said frame is retractable to a contracted configuration wherein said pivot axes of all said link pairs are located in a common plane.

5. A lazy tong frame according to claim 4 wherein:

said crossing link arms have surfaces which abut in said folded positions.

6. A lazy tong frame according to claim 5 wherein:

said surfaces comprise edge surfaces of said links located in said common planes containing the pivot axes of the respective links.

7. A nesting three-dimensional lazy tong structure of hollow polygonal crom-section, comprising:

a number of lazy tong frame forming the sides, respectively,

of structure;

each frame comprising a number of link pairs each including a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions;

a center pivot joining said central link portions on a center pivot axis normal to said intervening plane;

each link having relatively short and long arms at opposite sides of its center pivot, and said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one another;

said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane;

said link pairs being arranged end to end in lazy tong fashion with their center pivot axes parallel to one another and located in a common plane and with said short arm end portions of each link pair located opposite said long arm end portions of the adjacent link pair;

end pivots joining the adjacent link end portions of adjacent link pairs on end pivot axes parallel to said center pivot axes;

the corresponding end pivots of each link pair being equally spaced from the center pivot of the respective link pair, and the pivot axes of each link being located in a common longitudinal plane of the respective link;

said links diminishing in length in the direction of one end of the frame, whereby said frame is tapered and narrows in the direction of said one end, and the pivotally joined link arms of adjacent link pairs have equal length;

said frames being arranged edge to edge in a hollow polygonal configuration with the narrow ends of said frames at the same end of said structure;

rigid corner brackets joining the adjacent end pivots of adjacent frames; and

said structure being retractable to a contracted configuration wherein the tiers of said structure nest one within the other and all the pivot axes of said structure are located in a common plane normal to the longitudinal axis of said structure.

8. A structure according to claim 7 wherein:

said structure has a generally triangular crosvsection and includes three lazy tong frames.

9. A structure according to claim 7 wherein:

each said frame includes a pair of end links at each frame end equal in length to the adjacent link arms, pivot means joining one end of each pair of end links to the end portions of the adjacent link arms on pivot axes parallel to the remaining frame pivot axes, and pivot means joining the opposite ends of said end links on a pivot axis parallel to the remaining frame pivot axes.

W. A structure according to claim 9 including:

mounting brackets and a support at the wide and narrow ends. respectively, of said frames and pivotally joined to said opposite ends of said end links by the adjacent end link pivots.

# I i t i 

1. A link pair for a lazy tong frame comprising: a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions; a center pivot joining said central link portions on a center pivot axis normal to said intervening plane; each link having relatively short and long arms at opposite sides of said pivot; said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one another; said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane; said short arm end portions having end pivot means with pivot axes parallel to and equally spaced from said center pivot, and said long arm end portions having end pivot means with pivot axes parallel to and equally spaced from said center pivot, the pivot axes of each link being located in a common longitudinal plane of the respective link; and said links being rotatable about said center pivot to folded positions wherein said pivot axes are located in a common longitudinal plane of said links.
 2. A link pair according to claim 1 wherein: said crossing link arms have surfaces which abut in said folded positions.
 3. A link pair according to claim 2 wherein: said surfaces comprise edge surfaces of said links located in said common planes containing the pivot axes of the respective links.
 4. A lazy tong frame comprising: a number of link pairs each including a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions; a center pivot joining said central link portions on a center pivot axis normal to said intervening plane; each link having relatively short and long arms at opposite sides of its center pivot, and said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one another; said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane; said link pairs being arranged end to end in lazy tong fashion with their center pivot axes parallel to one another and located in a common plane and with said short arm end portions of each link pair located opposite said long arm end portions of the adjacent link pair; end pivots joining the adjacent link end portions of adjacent link pairs on end pivot axes parallel to said center pivot axes; the corresponding end pivots of each link pair being equally spaced from the center pivot of the respective link pair, and the pivot axes of each link being located in a common longitudinal plane of the respective link; said links diminishing in length in the direction of one end of the frame, whereby said frame is tapered and narrows in the direction of said one end, and the pivotally joined link arms of adjacent link pairs have equal length; and said frame is retractable to a contracted configuration wherein said pivot axes of all said link pairs are located in a common plane.
 5. A lazy tong frame according to claim 4 wherein: said crossing link arms have surfaces which abut in said folded positions.
 6. A lazy tong frame according to claim 5 wherein: said surfaces comprise edge surfaces of said links located in said common planes containing the pivot axes of the respective links.
 7. A nesting three-dimensional lazy tong structure of hollow polygonal cross-section, comprising: a number of lazy tong frame forming the sides, respectively, of structure; each frame comprising a number of link pairs each including a pair of similar links having mutually parallel central portions arranged side by side at opposite sides of an intervening plane passing between and parallel to said link portions; a center pivot joining said central link portions on a center pivot axis normal to said intervening plane; each link having relatively short and long arms at opposite sides of its center pivot, and said short arm of one link and said long arm of the other link extending across said intervening plane, whereby said latter arms crossover one another; said short link arms having end portions in a common plane parallel to and located at one side of said intervening plane, and said long link arms having end portions in a common plane parallel to and located at the opposite side of said intervening plane; said link pairs being arranged end to end in lazy tong fashion with their center pivot axes parallel to one another and located in a common plane and with said short arm end portions of each link pair located opposite said long arm end portions Of the adjacent link pair; end pivots joining the adjacent link end portions of adjacent link pairs on end pivot axes parallel to said center pivot axes; the corresponding end pivots of each link pair being equally spaced from the center pivot of the respective link pair, and the pivot axes of each link being located in a common longitudinal plane of the respective link; said links diminishing in length in the direction of one end of the frame, whereby said frame is tapered and narrows in the direction of said one end, and the pivotally joined link arms of adjacent link pairs have equal length; said frames being arranged edge to edge in a hollow polygonal configuration with the narrow ends of said frames at the same end of said structure; rigid corner brackets joining the adjacent end pivots of adjacent frames; and said structure being retractable to a contracted configuration wherein the tiers of said structure nest one within the other and all the pivot axes of said structure are located in a common plane normal to the longitudinal axis of said structure.
 8. A structure according to claim 7 wherein: said structure has a generally triangular cross-section and includes three lazy tong frames.
 9. A structure according to claim 7 wherein: each said frame includes a pair of end links at each frame end equal in length to the adjacent link arms, pivot means joining one end of each pair of end links to the end portions of the adjacent link arms on pivot axes parallel to the remaining frame pivot axes, and pivot means joining the opposite ends of said end links on a pivot axis parallel to the remaining frame pivot axes.
 10. A structure according to claim 9 including: mounting brackets and a support at the wide and narrow ends, respectively, of said frames and pivotally joined to said opposite ends of said end links by the adjacent end link pivots. 